The overall organization of urinary acidification has been defined by a variety of studies of the intact kidney and individual nephrons in vivo, yet relatively little is known about the transport precesses across the cell membranes, their biochemical nature, their rate-limiting factors and their organization within the epithelial cell layer. The proposed research extends our work on the control of the rate of urinary acidification in the turtle urinary bladder and focuses on the nature of the transport processes across the individual cell membranes, i.e. the proton pump at the luminal membrane and the efflux of the bicarbonate across the serosal membrane. The biochemical characteristics of the proton pump will be explored during anaerobiosis in the intact epithelium in vitro as well as as in a vesicle preparation of luminal membrane. The studies are designed to test the possibility that the pump is a plasma membrane proton-translocating ATPase and to distinguish its function from mitochondrial ATPase. The disposition of OH minus generated in series with H plus pump and the exit step for OH minus and/or HCO3 minus across the serosal membrane will be examined. In a closely related effort, we will study the role of the cellular (OH minus) as determinant for the rate of H plus secretion. The net rate of acid secretion by the intact epithelium is modified by a second active transport system which secretes HCO3 minus by an electroneutral mechanism in exchange for absorbed Cl minus. The nature of this transport system and its apparent independence of the transport pathway in series with H plus pump will be explored by physiologic as well as morphologic techniques.